The invention relates to an organic electroluminescent display device (OLED), which comprises a front electrode member, a counterelectrode member, an organic electroluminescent member arranged between the front electrode member and the counterelectrode member, and a protective layer of an inorganic barrier layer material.
LEDs in accordance with the state of the art customarily are inorganic semiconductor diodes, i.e. diodes whose emitter material is an inorganic semiconductor, for example ZnS, silicon, germanium or a III-V semiconductor such as InP, GaAs, GaAlAs, GaP or GaN with suitable dopants.
As a result of the availability of semiconductive, organic, conjugated polymers and the detection that they could suitably be used to manufacture light-emitting components, persons skilled in the art all over the world embarked upon the development of organic electroluminescent diodes and, based upon said organic electroluminescent diodes, the development of displays. Unlike inorganic LEDs, the application of which in displays having a comparatively high resolution is subject to certain conditions and involves high costs, organic electroluminescent diodes are attributed an enormous potential for small, easy-to-use displays.
Unlike liquid crystal displays, organic electroluminescent displays also have the advantage that they are luminescent and hence do not require an additional backlighting source.
As a result, said organic electroluminescent displays are employed in applications where luminescent display devices with a low supply voltage and low power dissipation are required. Said applications include, in particular, displays for mobile use such as cellular phones, organizers or applications in automobiles, i.e. from radios to navigation systems.
A serious problem however remains the service life of the organic electroluminescent display devices that is too short. In particular, it is a drawback that the luminance of the display devices decreases in a non-uniform manner over the surface during operation of the device. Also when the display device is not in operation, dark spots in the electroluminescent layer occur in the course of time. These dark spots are caused, and the expansion thereof enhanced, by moisture and detrimental gases from the surrounding atmosphere.
In order to seal organic electroluminescent display devices so as to protect them from moisture and detrimental gases, various arrangements comprising a gastight housing or moisture-absorbing means in the housing were proposed.
For example, U.S. Pat. No. 6,160,346 describes an electroluminescent device with an electroluminescent component that comprises an electroluminescent organic layer and two electrodes in contact with said electroluminescent layer, said electroluminescent component being enclosed in a housing composed of inorganic barrier-layer materials comprising a metal having a low melting point or an alloy having a low melting point below approximately 250xc2x0 C. The housing seals the electroluminescent member in an airtight and waterproof manner.
A drawback of this electroluminescent device resides in that, in reaction to mechanical damage to the house, the device is subject to plastic deformation.
It is an object of the invention to provide an organic electroluminescent device comprising a mechanically and chemically stable protective layer that serves as a reliable diffusion barrier to moisture.
In accordance with the invention, this object is achieved by an organic electroluminescent display device comprising a front electrode member, a counterelectrode member, an organic electroluminescent member arranged between the front electrode member and the counterelectrode member, and a protective layer of an amorphous carbon modification.
This protective layer forms a coherent material layer that is used as a hermetic packing to protect the display device against environmental influences such as moisture and mechanical loads.
Said protective layer forms an excellent barrier against the penetration of water vapor and other contaminating or corrosive substances, and it is insensitive to mechanical deformation, crack formation and scratches.
It is preferred that the resistivity of the protective layer xcfx81xe2x89xa7106 xcexa9cm.
It is also preferred that the layer thickness of the protective layer dxe2x89xa65 xcexcm. In some applications, layer thicknesses of 50 nm may already provide sufficient protection.
The invention relates to a method of manufacturing an organic electroluminescent display device comprising a front electrode member, a counterelectrode member, an organic electroluminescent member arranged between the front electrode member and the counterelectrode member, and a protective layer of an amorphous carbon modification, in which the protective layer is deposited from the gas phase.
In accordance with a preferred embodiment of the invention, the protective layer is deposited by means of a microwave-plasma-CVD-process.
It is particularly preferred that the operating point of the deposition from the gas phase lies in the kinetically controlled range.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.